ECM216 BUILDING SERVICES

EDITED BYAZUAN AHMAD FAUZI 2011803188 UITM PULAU PINANG MAC 2013

ECM 216

AIR-CONDITIONING SYSTEM

LEARNING OUTCOMEAt the end of the lecture the student will be able to:

Explain the important of Air-conditioningSketch and explain the process of cooling the airDescribe the function of compressor, condenser, expansion valve and evaporatorDistinguish between split unit and central unit of air-conditioningExplain the function of AHU, Chiller and cooling towerShow the heat transfer in air-conditioning system

IntroductionAir-conditioning is the process of cooling the air in a building to provide a comfortable temperature. It is divided by two, forced air conditioning system and hydronic (hydronic is the name for the use of water as the heat-transfer medium in heating and cooling systems) air conditioning system.

Types of an air conditioning system

Advantages of an air conditioning systemImprove working efficiency, reduce illness and absenteeism (absenteeism is a habitual pattern of absence from a duty or obligation).

Increase sales, productivity and comfortness.Less cleaning, material and furniture last longer.Suitable environments for plants grow process, electronic and lab areas.Reduce internal and external pollution e.g. dust, noise and smokeLess risk of fire or damage due to static electricity caused by dry air

Factors of choosing types of systemSize – volumeUsage – people, processArrangement of rooms, buildingsBuilding materials – heat retainedWater or air for releasing heat from condenserNoise level of system usedReliability, installation, cost & maintenanceFlexibility or user friendly

An air cycleAn air cycle is the process of distributing the clean air to the particular room to be cooled. The purpose of cycle is actually removes heat from that room.Removed heat in this cycle occurs when the return supply air are absorb at the condenser. The heat condensing medium using either air or water. So, this cycle have supply distribution and return distribution.The method of this distributing might be using air ducting or cooling water piping.Complete system of an air conditioner need the refrigeration cycle and air cycle. In air cycle there is a few component to be use such as:

a) Air Handling Unitb) Air Filterc) Air Ductingd) Clean air inlete) Humidification Equipmentf) Dehumidification Equipment.

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ECM 216

RefrigerantA refrigerant is a compound used in a heat cycle that undergoes a phase change from a gas to a liquid and back. The two main uses of refrigerants are refrigerators/freezers and air conditionersThe most widely used refrigerants were the halomethanes R-12 and R-22, with R-12 being more common in automotive air conditioning and small refrigerators, and R-22 being used for residential and light commercial air conditioning, refrigerators, and freezers.

AIR CONDITIONING COMPONENTS1. compressor2. evaporator3. condenser4. expansion valve

BASIC AIR-COND SYSTEMRefrigeration cycle

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ECM 216

AIR-CONDITIONING COMPONENTS1. Evaporator2. Compressor3. Condenser 4. Expansion Valve5. Air Handling Unit 6. Chiller

EVAPORATOR Evaporator coils of air conditioning systems are sometimes called cooling

coils. They are also used in air-handling units. They contain chilled water. They are completely different from those used in

direct expansion air-Cond units. So cooling coils is not an accurate word to use in small air-cond units. Evaporator coils should be used instead.

Evaporator tubes must contain refrigerant liquid that can evaporate to become gas.

In an air conditioning system, when the liquid refrigerant absorbs heat, it turns to gas. The heat is thus transferred to the refrigerant.

That's how the heat is moved from one location to another location. The evaporator coils are located in the low-pressure system of a refrigeration circuit.

COMPRESSOR Purpose of the compressor is to circulate the refrigerant in the system under

pressure, this concentrates the heat it contains. At the compressor, the low pressure gas is changed to high pressure gas. This pressure build up can only be accomplished by having a restriction in the

high pressure side of the system. This is a small valve located in the expansion valve.

CONDENSER Is a heat exchanger that removes heat from high pressure refrigerant vapour.

High pressure refrigerant vapour flows through the condenser and a condensing medium passes across the outside of the condenser.

Heat flows from the hot refrigerant vapor to the cold condensing medium. A condensing medium is a fluid (air or water) that has a lower temperature

than the refrigerant, which causes heat to flow to the medium. A condensing medium removes heat from a refrigerant because it has a

lower temperature than the refrigerant. Air and water condensing mediums used in refrigeration system. As a refrigerant vapor gives up heat to the condensing medium in a

condenser, the vapour condenses to a liquid.

1. Low pressure liquid refrigerant in evaporator absorbs heat and changes to a gas

2. The superheated vapour enters the compressor where its pressure is raised

3. The high pressure superheated gas is cooled in several stages in the

4. Liquid passes through expansion device, which reduces its pressure and controls the flow into the evaporator

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ECM 216

EXPANSION VALVE Refrigerant enters the inlet & screen as a high-pressure liquid. Refrigerant

flow is restricted by a metered orifice through which it must pass. As the refrigerant passes through this orifice, it changes from high-pressure

liquid to low-pressure liquid (passes from high side to low side of the system). Expansion valve removes pressure from the liquid refrigerant to allow

expansion/change of state from a liquid to a vapour in the evaporator. High-pressure liquid refrigerant entering the expansion valve is quite warm.

The liquid refrigerant leaving the expansion valve is quite cold. The orifice within the valve does not remove heat, but only reduces pressure.

SELF CONTAINED (LOCALISED)Most central air conditioning units operate by means of a split system because of;

Low-cost Results in reduced noise inside the house. (at the expense of increased noise outside the house).

SPLIT UNIT• Are perfect for those that do not have central air conditioning & do not want

to settle for the noise & inefficiency of window units.• Offer higher efficiency & reduced noise without a large hole in the wall/ an

open window. • By separating the compressor & condenser coil from the fan & evaporator

coil, the noisiest component is away from the room.• The indoor unit will usually have remote control capabilities and a timer to

cycle the system only when needed. The indoor unit is called an air handler because it has the evaporator coil, blower & controls inside.

• The outdoor unit is called the condenser. • They are connected together with refrigerant piping & control wiring, similar

to a central system.• Since mini splits have no ducts, they avoid the energy losses associated with

ductwork of central forced air systems. • Duct losses can account for a significant portion of energy consumption for

space conditioning, especially if the ducts are in a unconditioned space such as an attic.

• “hot” side( condensing unit): including condensing coil, compressor and fan- situated outside home.

• Consists of a long, spiral coil cylinder shaped. Inside the coil – fan: blow air through the coil, along with a weather-resistant compressor and some control logic.

• "cold" side : consists of an expansion valve and a cold coil, and it is usually part of your furnace or some type of air handler.

• Furnace blows air through an evaporator coil, which cools the air. This cool air is routed throughout your home by means of a series of air ducts.

•

WINDOW UNIT Compressor, evaporator, condenser and expansion valve are in a compact unit

at the wall. Suitable for individual rooms or offices with at least one external wall. Only disadvantages of window units are noisy, no fine control of temperature

and humidity and higher consumption of electricity per ton. Ideal when only a few rooms are to be cooled and individual controls are

required. Initial cost is low.

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THE ADVANTAGE AND DISADVANTAGE OF SPLIT AND WINDOW UNIT

Split Unit Window UnitAdvantage Disadvantage Advantage Disadvantage Silent No need to hack

the hack

More expensive Need to install

piping from inside to outside component

Evaporator and fan inside building, compressor outside building

Cheaper No need to install piping

All component sit under one compartment

Need to hack the wall

noise

CENTRAL PLANT PACKAGE• There are basically two types of package system – air-cooled or water-cooled • Generally used with ductwork. • Provide better control than window units - have more than one compressor,

cylinder unloading compressors, split coils, time delay starters, etc.

AIR-COOLED Consist of multi stage blower like window unit. It is located in one big room or outside the building. Cooling capacities and volume of air delivered by the units would depend

on individual manufacturers. Generally for air-cooled packed units the cooling capacities are from

about 2 tons to about 20 tons (2 HP to 30 HP). The nominal delivery volume of air delivered is about 500 cfm per ton. Split into the compressor condenser section and the fan coil section -

provides more flexibility in equipment placement but the distance between these two sections should not be too much or the refrigerant piping sizes would have to be increased.

Overall efficiency of packages units 7 to 11 btu/hr per watt for air cooled packaged units

WATER-COOLED• Consist of AHU and blower chilled.• Consist of compressor, condenser, expansion valve and evaporator.• For water-cooled packed units, the cooling capacities are from about 2 tons

to about 50 tons (2 HP to 60 HP)• The overall efficiency of packages units range from 9 to 15 btu/hr per watt for

water cooled equipment.

AIR HANDLING UNIT (AHU)• AHU is function for the process of heating, cooling, humidification,

dehumidification, air filtering and air distribution.• Therefore, it is also reprocess the return air from particular cooled room

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ECM 216

Type of AHU

Air Handling System with Pleated Panel Filters: Air Handling units have coils much like air conditioning units as shown above.

So it is important to keep these clean by having the filters changed on a regular basis. Also, the belts wear down quite easily and can snap causing the whole system to fail if left unchecked.

CHILLER Unit where chilled water is cooled by the evaporator. The chilled water is circulated inside the cooling coil in the AHU, being

warmed and to the chiller. Inside the chiller, the low pressure liquid refrigerant inside the evaporator

absorbs heat and flows to the condenser. The condenser is either air-cooled or water-cooled. This unit is usually installed for central plant system.

COOLING TOWER used in central air conditioning systems. function - to cool the warm water from the chiller condenser. heat from the rooms in a building is transferred to chilled water, then transferred

into the refrigerant, and finally to the cooling water. The cooling tower is at the final point of the heat transfer. The heat is transferred to the atmosphere.

ECM216 BUILDING SERVICES

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ECM 216

heat in the cooling water is removed by letting moving air come into contact with it.

Water is normally spread out and allowed to drop down by gravity from a height. Plastic fillings are arranged so as to increase the wetted surface of the water while

it is dropping, while at the same time provide better contact between the air passages and the water.

PHYCHROMETRIC Is the graph that’s the behavior of mixture of air and water vapours. It simple air calculation and through plotting we would be able to understand

condition of air after going through various processes The coordinates show the lines of

o wet bulb temperatureo dry bulb temperatureo moisture contento relative humidityo specific enthalpyo specific volume of air

Wet Bulb Temperature-unit °C Air temperature measured by normal thermometer whereby the end of bulb is

wrapped with net muslin cloth, measuring air temperature not less than 3 m/s.

Dry Bulb temperature-unit °C The actual temperature of air as measured by an ordinary thermometer

Relative Humidity-unit % stage Total humidity of existing air content compare to max humidity that the air can

absorb at particular temperature(same temperature)

Relative humidity= total moisture content of airMaxmoisture content absorbedby air at a particular temperature

Sensible Heating Heating of air without adding moisture

Sensible heating without humidification The air entering the room is heated to required temperature without adding its

moisture content

Sensible cooling Cooling of air without dehumidification

Sensible cooling without dehumidificationThe air entering the room is cooled by dehumidifying through cooling, washing and

reheating

Specific Enthalpy-unit kcal/kg Thermodynamic calculation as being the same as it content or heat contained in

unit weight of distance

Absolute humidity-unit kg/kg Weight of water vapour existed in humid air compared to weight of dry air in the

humid air

Specific volume-unit m/kg The unit weight of dry air plus it associates water vapour

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ECM 216

CONCLUSION The design objective of air-conditioning system is to control indoor parameters

within required thermal comfort and indoor air quality overall. The air conditioning system is the one most important devices to give the fresh

air especially in house and room.